An Oxido‐Bridged Diiron(II) Complex as Functional Model of Catechol Dioxygenase

Abstract

An oxido‐bridged diiron(II)‐phenanthroline complex, [Fe2O(phen)2Cl2] (1) [phen =1,10‐phenanthroline] has been synthesized from an oxido‐bridged diiron(III) precursor in presence of sodium azide and structurally characterized by different spectroscopic tools including single crystal X‐ray diffraction study.From X‐ray crystal structure of 1, it is revealed that each of the Fe(II) centre is in distorted octahedral geometry with FeN4OCl core and the molecule crystallizes in Pnc2 space group. Bond valence sum (BVS) calculation confirms the existence of iron ions in +2 oxidation state in 1. The diiron(II) complex has been evaluated as model system for the catechol dioxygenase enzyme by using 3,5‐di‐tert‐butylcatechol (DTBC) as the substrate in acetonitrile medium, revealing that 1 efficiently mimics the catalytic cycle of catechol dioxygenase. Upon stoichiometric addition of DTBC pretreated with two equivalents of triethylamine (Et3N) to the diiron complex, two catecholate‐to‐iron(III) LMCT bands (515 nm and 734 nm) are observed. The in situgenerated catecholate adduct from 1in acetonitrile solution react with dioxygen to afford exclusively extradiol cleavage products along with a small amount of benzoquinone, which is also discerned from the appearance and decrease in intensity of the electronic spectral bands around (708 nm; 507 nm) nm. Nucleophilic attack by molecular oxygen on catecholate adduct in solution provides substantial evidence for the regioselective extradiol cleavage products.